1. Field of the Invention
The present invention relates to hydrogen storage and, more particularly, to a composition and method for hydrogen storage.
2. Description of Related Art
Hydrogen has long been regarded as a promising source of fuel, both as a replacement for conventional hydrocarbon fuels and as a fuel for alternative energy technologies, such as fuel cells. The lightest element, hydrogen has a very high energy-to-weight ratio, and can be combusted cleanly, without carbon monoxide or dioxide byproducts. Unfortunately, storing and transporting useable quantities of hydrogen present difficult problems that are significant barriers to the commercial use of hydrogen as a fuel.
A common technique for storing large quantities of hydrogen is a liquefaction process by compressing and cooling hydrogen from a gas phase into a liquid phase. At ambient pressure, hydrogen gas liquefies at 20 K (i.e., xe2x88x92253 C), and approximately 70 g/L of the hydrogen gas can be stored in the liquid phase. However, the liquefaction process is very energy intensive. For example, the energy used to compress hydrogen gas into a liquid may be as much as 40% of the energy that is within the gas itself. In other words, an additional amount of energy equivalent to about 40% of the energy capable of being expended from the hydrogen gas is needed to liquefy the hydrogen. Further, liquid hydrogen should be maintained at 20 K to prevent the liquefied hydrogen gas from boiling off and causing problems due to the increased gas pressure. Maintaining the liquid hydrogen at 20 K requires specially designed insulated containers and very careful handling.
Another common technique for storing hydrogen is to compress the gas into a suitable vessel. For example, a gas tank pressurized to 35 MPa can store 15 g/L of hydrogen. However, a pressurized-gas tank is heavy and cumbersome. In addition, the circumstances for the transport and use should be carefully controlled to address all of the safety issues for a highly-compressed volatile gas.
Other techniques for hydrogen storage involve chemically bonding hydrogen molecules to a host material. This type of hydrogen storage is being actively investigated, and various materials have been shown to be suitable storage hosts for hydrogen. For example, metals and carbon nanotubes have both been reported as suitable host materials. However, there are still many remaining technical problems, such as the high temperatures required for releasing hydrogen from a metal hydride, to be overcome before the realization of commercial realization of hydrogen storage.
Gas hydrates are solid compounds with xe2x80x9cguestxe2x80x9d gas molecules trapped in H2O frameworks that are formed at low temperature while at either a high or ambient pressure. In one set of gas hydrates, water molecules form hydrogen-bonded xe2x80x9ccagesxe2x80x9d around xe2x80x9cguestxe2x80x9d gas molecules to form a clathrate in which the cage structures are either sI, sII or sH type. In other gas hydrates, the xe2x80x9cguestxe2x80x9d gas molecules fill in the structural cavities of specific phases of ice, and are commonly called xe2x80x9cfilled icexe2x80x9d. Two types of gas hydrates, denoted as C1 and C2, have been reported at high pressures as discussed in Vos et al., xe2x80x9cNovel H2xe2x80x94H2O Clathrates at High Pressures,xe2x80x9d Physical Review Letters, 71, pp. 3150-3153, 1993, the disclosure of which is hereby incorporated by reference herein in its entirety. Although the C1 and C2 types of gas hydrates store significant amounts of hydrogen, such as approximately 23 g/L for C1 and approximately 110 g/L for C2, the extremely high pressures, such as greater than 700 MPa for C1 and greater than 2250 MPa for C2, required to form and store the compounds makes them commercially unsuitable, as well as a safety risk.
One of the present inventors is a co-author of the Vos et al. article, in which C1 and C2 are described as xe2x80x9cnovel clathratesxe2x80x9d because, for example, they do not have the classical sI, sII or sH clathrate cage structure. Although this article refers to C1 and C2 as xe2x80x9cclathrates,xe2x80x9d it has since been confirmed that C1 and C2 are not in fact classical xe2x80x9cclathratesxe2x80x9d under at least some commonly-used definitions. Thus, to avoid any confusion, and for purposes of this application, the term xe2x80x9cclathratexe2x80x9d as used herein shall be as defined below in the detailed description of the preferred embodiments.
The hydrogen storage mechanism remains a key challenge for practical usage of hydrogen as a general fuel.
Accordingly, the present invention is directed to a composition and method for hydrogen storage that substantially obviates on or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a composition and method for hydrogen storage at or near-ambient pressure and at a moderate cryogenic temperature.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
An exemplary embodiment of a method for hydrogen storage in accordance with the present invention includes providing water and hydrogen gas to a containment volume, reducing the temperature of the water and hydrogen gas to form a hydrogen clathrate at a first cryogenic temperature and a first pressure, and maintaining the hydrogen clathrate at second cryogenic temperature within a temperature range of up to 250 K to effect hydrogen storage.
In another exemplary embodiment, a method for hydrogen storage includes providing a containment volume having a specified volume, partially filling the containment volume with water, providing hydrogen gas to the specified volume, cooling the containment to a first cryogenic temperature in a cryogenic temperature range of up to 250 K to form a hydrogen hydrate and maintaining the hydrogen hydrate within pressure range of 35 MPa to 0.01 MPa to effect hydrogen storage.
In another exemplary embodiment, a method for hydrogen storage includes providing a containment volume having a specified volume, partially filling the containment volume with water, providing hydrogen gas to the containment volume, pressurizing the containment volume to a first pressure within a pressure range of 100-600 MPa, cooling the containment volume to a first cryogenic temperature within a moderate cryogenic temperature range of 77 K to 250 K to form a hydrogen hydrate, quenching the first pressure in the containment volume to a quenched pressure within a pressure range of 35 MPa to 0.01 MPa and maintaining the hydrogen hydrate within the moderate cryogenic temperature range to effect hydrogen storage.
In another exemplary embodiment, a low-pressure hydrogen clathrate includes H2O molecules, H2 molecules and a unit cell including polyhedron cages of hydrogen-bonded frameworks of the H2O molecules built around the H2 molecules.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and intended to provide further explanation of the invention as claimed.